There is never an isolated pole (a monopole). All magnets attract iron, such as that in a refrigerator door. The two poles are thus named the north magnetic pole and the south magnetic pole (or more properly, north-seeking and south-seeking poles, for the attractions in those directions).

The end that faces the north is called the north-seeking pole, or north pole, of the magnet. When two magnets are brought together, the opposite poles will attract one another, but the like poles will repel one another. This is similar to electric charges. Like charges repel, and unlike charges attract.

No, the magnetic field lines inside the bar magnet are non-uniform. They are curved in the nature.

Elevated temperature: Magnetic materials lose magnetism as they heat, but they regain magnetism when cooled provided the maximum temperature is below their Curie temperature. Above the Curie temperature, a magnet permanently loses all or some of its magnetism.

A magnet can be re-magnetized by rubbing a neodymium pole, for example, against the opposite pole of the old magnet, thus repeating with the other side and achieving the desired effect. After this process, any magnet that has lost its magnetic properties can become fully functional again.

As the temperature increases, at a certain point called the Curie temperature, a magnet will lose its strength completely. Once the metal cools, its ability to attract magnets returns, though its permanent magnetism becomes weak.

Magnets are surrounded by an invisible magnetic field that is made by the movement of electrons, the subatomic particles that circle the nucleus of an atom. Magnets attract when a north pole is introduced to a south pole. If like poles are introduced, either north to north or south to south, the magnets repel.